The goal of this project is to determine some aspects of the organization and the evolutionary and maturational development of the visual system of vertebrates with particular reference to midbrain mechanisms. Electrophysiological studies are planned to reveal specialization in different mammalian species of neuronal responses to stationary and moving stimuli, directional and velocity selectivity, ocular dominance, maturational changes in a given species and the influence of cortical structures on collicular organization. Comparative studies in cat, golden hamster and rhesus monkey are planned. A parallel study of the maturation of these same properties in newborn kittens is planned with emphasis on the role of corticotectal influences on the development of collicular neuron properties. Morphological analyses deal with the precise labinar distribution of collicular neurons of various types and the spatial organization of the pretectal nuclear group. Neurons labelled with radioactive amino acids will be employed for study of fast axonal protein transport to determine the precise projection of small neuronal population in the cat and hamster.